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Are there roll control devices other than ailerons?
With the little that I've learnt about aeroplanes, I know that the aileron is the control surface that a pilot use to roll the plane by decreasing the lift of one wing and increasing the lift of the other wing. And it's (aileron) generally located at the wing trailing edge.
Now, if the wing tip is made flexible (or hinged to the wing), can the wing tip serve the purpose of an aileron by lifting the wing tip upward or downward?

If it is hinged people would still call it an aileron

@ymb1 Tip noted.

Yes, that will work. If the entire wing tip pivots, it simply acts as an aileron that takes up the entire chord of the wing.
Other alternatives to ailerons include:

Weight shifting. If you can shift the aircraft's center of mass left and right a significant amount, thus will cause the aircraft to roll in the same direction. This is how hang gliders turn.
Wing warping. Essentially the same thing as ailerons, but accomplished by bending or warping the wing rather than by pivoting a hinged piece of the wing. Early Wright aircraft did this, but I don't know of any modern aircraft that do. (Birds probably do this, too.)
Roll spoilers. By deploying a spoiler on just one wing, you'll cause the aircraft to roll in the same direction. Some airliners do this some of the time.
Sliding the wings left and right. Okay, I admit that I don't actually know of any aircraft whatsoever that do this. But if you were to slide an aircraft's wings left or right, that would cause it to roll in the opposite direction.
Cyclic pitch control. Only rotary-wing aircraft (such as helicopters) can do this. The rotor blades can be configured to change pitch depending on where they are in the cycle, and this can produce a roll. Cyclic pitch control is the main way that helicopters are controlled.
Yawing and using the dihedral effect. An aircraft doesn't actually need any roll controls at all if the wings have a significant dihedral angle. Instead, you can roll the aircraft by yawing it into a sideslip; the dihedral effect responds to the sideslip by rolling the aircraft. A lot of RC aircraft use this method, as does at least one ultralight aircraft, but it's not a great way to go, because sideslips produce drag, and they can produce a "snap roll" in the event of a stall.

Wow! What a great answer.

The MU-2 is totally reliant on spoilers for roll control, BTW. (it's part of why it requires special training -- normal techniques for stall/spin recovery don't apply as a result of this)

@UnrecognizedFallingObject  I've been thinking about the resulting stall/spin  characteristics of an aeroplane that uses this wingtip device for rolling instead of the conventional aileron. Will the stall/spin handling procedures be identical to other planes that use aileron? Should I ask this in a separate question?

Roll spoilers and dihedral effect are also used in airliners as a backup for ailerons.

Roll spoilers also don't create adverse yaw, which is advantage for flying wings that have limited options for compensating it.

@JanHudec the problem with roll spoilers is pro-verse yaw (to varying degrees), so you still need a yaw damper, or if you don't have one, you have to learn to squeeze in small amounts of opposite rudder in turns with large roll inputs.

Barnes Wallis experimented with a variant of your 4th point : using variable geometry on each wing for roll control. He took it a bit further to eliminate the tail (and its drag) too. Wildgoose flew (as a pilotless prototype), Swallow was a design concept. AFAIK all later variable geometry (F111, Tornado etc) just used it to adjust wing sweep.


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Do Vx and Vy speeds refer to IAS or TAS?
I've had this discussion with my FI: Are speeds such as Vx and Vy referring to IAS at all times or TAS that needs to be compensated for?
Here's an example. Let's assume the following:

Vy of my single piston engine, fixed prop aircraft is specified at 70 kts
I'm taking off from 0 ft MSL, climbing to 5000 feet pressure altitude
it's +15° celsius outside temperature with a QNH of 29.92 Hg / 1013 hPa (all ICAO standard)

Which of these two scenarios would actually get me to my target altitude faster?

I'm constantly pitching for 70 kts IAS under full power
I'm constantly pitching for 70 kts TAS under full power, i.e.:

70.0 kts IAS @ 0 ft
68.6 kts IAS @ 1000 ft (70 / 1.02)
67.3 kts IAS @ 2000 ft (70 / 1.04)
66.0 kts IAS @ 3000 ft (70 / 1.06)
64.8 kts IAS @ 4000 ft (70 / 1.08)
63.6 kts IAS @ 5000 ft (70 / 1.10)

I was assuming an appoximate increase of 2% per 1000 feet in TAS compared to IAS. My FI says that scenario two would actually yield in an optimal climb, but I'm uncertain as to how the reduced air density would affect lift and therefore the optimal speed to maintain.

IAS -- simply because the POH tries to present information in a form that is immediately useful to the pilot.  You need Vx and Vy quickly -- they show up as a mark on the airspeed indicator so you can quickly glance and know where you stand.
You need TAS when you're navigating -- figuring out how far you fly in a certain amount of time, don't forget winds, etc.  You likely don't fly at best climb speed or minimum sink speed for the extent of the mission.

Thank you! So IAS is to be used for the reasons you said, which makes a lot of sense, however is this also physically the optimum as you climb or would the gradient in scenario two actually result in a faster climb?

That gets down to subtle details of how the engine and propeller performance changes with altitude.  What we know for sure -- at the absolute ceiling, Vx is equal to Vy -- no matter whether they are measured in IAS or TAS.  Consequently, one or the other (or both) must vary with altitude.
Fortunately, this variation is relatively slow and we mostly care about the value of Vx and Vy near the ground.

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What to log as consecutive number of flight for aircraft logbook?
In GA flying as part of flight clubs, how do you usually number the flights logged in the aircraft logbook? At my local club, they increase the number by the amount of landings performed. So for instance, you may have a single flight with one touch-and-go, one full stop landing. The line in the log book would read 10,787 - 10,788 for two landings.
Is this common practice, and why? Would you not usually number every entry through one by one?

Are you suggesting that if you logged 10 touch and goes on a single flight that it would be preferable to enter each one on a separate line?  Because that doesn't make sense, and would really string out the log book.  Standard practice in most log books is one line per "flight", however you choose to define that.  P.S.  I have been in several flying clubs and none have logged landings.  It's completely up to the club to decide this sort of thing, and I think any answer would be opinion based.

@MichaelHall He's in Germany and is referring to an aircraft log book where flights are recorded, not done in the US. In Canada we call it the Journey Log and every a/c has to have one. When you buy an airplane in Canada you have a complete record of all of its flights. If it's a homebuilt, like mine, you can use the J Log to record all maintenance as well, and skip the technical logs. The airplane's entire operating and maint history in one book. Anyway it looks like German requirements are to record TO/LDG cycles. In a Cdn JL you record each departure (and dest if CC) location as a flight.

@MichaelHall Not quite, if you logged 10 touch and goes the column for # of flight would read 10787 - 10797. In my mind it should only ever increase by one, but in this case it increases by the number of landings performed.

@DoubleM in the Transport Category world, takeoffs and landings, flight cycles, are a more important metric than total hours, mainly because most structural fatigue issues, and some system life issues, are more determined by up/down cycles (loading/unloading the structure or system on/off) than total hours. That's the only reason I can see for recording individual TOs and LDGs for tracking purposes and is very unusual for a light aircraft where fatigue isn't really a concern. That kind of recording might just be a club policy for their own reasons.

"In my mind it should only ever increase by one." Ok, but why do you think that? What does "Ltd. Nr. des Fluges" mean? It seems apparent that the club expects pilots to log the number of landings in the appropriately labeled column, do you simply disagree with this practice? Or do you believe members should never practice touch and goes?  It's not really clear why you are asking this question...

@MichaelHall "Lfd. Nr. des Fluges" literally means "Consecutive Number of Flight", as in "this is the nth flight performed with this aircraft". By nature I expect it to increase by one each line. The reason I'm asking is because I'm building SaaS that has a digital logbook feature. I want to understand the requirement behind this practice, and to find out whether it's common or local, so I know how to best attend to the requirement if at all. Seems to me like the reason is simply because there is no dedicated column for landings in this particular book. Thanks for your Canadian perspective!

Well it should be simple then:  If you are creating a digital logbook just include a field for the number of landings and let the user decide whether it is desired or required to log them.  But don't call it "Lfd. Nr. des Fluges"!  ;)

@MichaelHall That's exactly what I'll do. Thank you for the help, Michael.

That appears to be a German operational log book. In Canada it's called a Journey Log. In the United States such a log is not required to be maintained, only the technical logs.  You should check with EASA requirements for Journey Logs.  In Canada you record the date, pilot's name, departure and arrival airport (which can be the same, obviously, if it's just a local flight), air time and flight time, and total accumulated air time.
The normal requirement when a Journey Log must be maintained is to record a flight as the period from engine start to shutdown, and thus touch and goes are not recorded as individual flights, unless the touch and go was at another airport.
The log book pictured appears to be designed to record flight cycles as well as total air time; perhaps that is a German requirement.

Thank you for taking the time to post such an elaborate answer, it's highly valuable to me. Very much appreciated!

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How to avoid rocking side to side after touchdown?
I'm a fresh student pilot with about 20 flight hours in an Aquila A210. One thing that sometimes seems to happen to me is that after touchdown, the plane slightly swerves to one side (I can feel it in the rudder pedals, too), which I instinctively try to compensate, but end up overcompensating and rocking the plane side to side instead - which is really not good.
I would like to know why this happens and how to avoid it, or react in case it does happen.
A theory I have is that I am already applying rudder input on short final to line the nose up with the runway, which from my understanding will also angle the nose wheel. Upon touchdown, that's where the plan will want to roll on the ground. Could this be the reason?
How do I fix it?

Is wikipedia right that your nosewheel is directly steerable, not free-castering?

@CamilleGoudeseune Correct, from my understanding it is directly steerable.

What does your CFI say?

@300D7309EF17 He says I should 'stop rocking the aircraft' or basically just 'not do it', but did not go fully into detail as to what initiates this behaviour in the first place that would help me avoid it entirely.

Have you asked him how to fix it? i.e., the same question you asked here.

@FreeMan Well yes, that was basically his reply. 'Just don't do it'.

My own airplane is like that, though it's a low wing with a wide oleo main gear and doesn't lean in turns. But it will turn to the side somewhat if a large rudder input is held through nosewheel contact.
A special technique is required when landing airplanes in crosswinds with a steerable nosewheel that has a direct, rigid linkage, as opposed to being connected via a bungee strut that provides springiness or compliance in the rudder pedal connection to the nosewheel (for example, in traditional trainer world, Cessnas use compliant connections, and Piper Cherokees are rigid).
You should be noticing that when the nose wheel contacts the runway while holding a rudder input, you feel the pedals jerk under your feet. If you are holding firm rudder pressure at the point of contact, your feet keep the wheel from fully aligning and the airplane darts to the side because the transition from rudder surface effect to wheel traction effect is immediate.
You need to relax the foot pressure on the rudder pedals about, say, half a second before you let the nosewheel make contact, so that the wheel can caster straight without impediment. Don't take your feet off, just ease off the pressure until you feel the pedals jerk straight under your feet, then resume only the pressure needed to keep tracking straight. With a bit of practice, it becomes automatic and you won't even notice yourself doing it.

That is extremely helpful, thanks so much for answering!


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How do I read this flight plan route?
When I create a flight plan using SimBrief, for example for London Gatwick (EGKK) to Dublin Airport (EIDW), it generates the following route:
NOVM1M NOVMA L620 NIBDA N14 MEDOG L18 ABLIN ABLI1L

So far I know that NOWM1M is the departure (SID) and ABLI1L is the arrival (STAR). In this case, NOVMA is the last waypoint of the departure and ABLIN is the first waypoint of the arrival. In a TBM9 aircraft for example, I can enter those routes into the FMS (G3000) by selecting it as the arrival and departure of the respective airports.
My question is about the waypoints in between: L620 NIBDA N14 MEDOG L18. As far as I understand, a waypoint's name should consist of exactly five alphanumerical characters. Those would then only be NIBDA and MEDOG. In Microsoft Flight Simulator 2020, I can find and add those waypoints as enroute waypoints. I can however not find L620, N14 or L18.
Also in the chart created by SimBrief, there are more waypoints plotted than appear in the list, such as KENET.
My questions are:

What are L620, N14 and L18, and why can I not find them in the FMS?
Why are there additional waypoints showing on the map that do not appear on the list?

Thank you for any clarification you can give.

Those are airways connecting the waypoints of your route. The map you show already includes all waypoints along the route (like e.g. KENET on airway N14). When filing such a route, you are expected to follow all these waypoints and not go direct between the waypoints in the route summary (e.g. NIBDA direct to MEDOG would look very different compared to airway N14).
One can enter all waypoints one by one without including the airway information. The full document from Simbrief will contain a long table with all waypoints. However, that is quite tedious and most modern flight management systems (FMS) will allow entering a route with airways. On the G3000, it works likes this:

Adding an individual airway to a flight plan:

For the active flight plan: From MFD Home, touch Flight Plan.
[...]
Scroll the list if necessary and touch a waypoint options button to display the 'Waypoint
Options' Window.
Touch the Load Airway Button to display the 'Airway Selection' Screen.
Touch the Sort A→Z Button to select/deselect alphabetical sorting of the airway
waypoints.
Scroll the list if necessary and touch an airway selection button to select the airway and
display the 'Select Exit' Window (if Sort A→Z is selected, the exit points are displayed in
alphabetical order, not the order they appear in the airway).
Scroll the list if necessary and touch an airway exit point selection button to select the
airway exit point. The airway waypoint sequence is now show on the 'Airway Selection'
Screen.
Touch the Load Airway Button to insert the airway into the active or standby flight plan.

(Garmin G3000 - Cockpit Reference Guide - TBM 930)
I do not know if the G3000 in MSFS2020 works this way, but support for the simulator is off-topic here.

Excellent answer, thank you. Unfortunately, the G3000 in MSFS2020 does not model that feature at this time, but now I finally understand how to read the flight plan correctly.

The enroute charts for UK are here. The waypoints and the airways are visible in ENR 6-68.

@DoubleM There are some older real-world FMSes that can’t do airways either, so bonus realism?


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Streamline Curvature Theorem applied to Airfoils?
I am new to studying aerodynamics and taking up aeromodelling and am currently learning how lift is obtained in-depth. When studying the two common explanations as to how lift is generated by an airfoil (Newton's Third Law & Bernoulli's Equation), I also came across something known by Japanese aerospace engineers as the "Streamline Curvature Theorem".
The Streamline Curvature Theorem is as follows: Pressure differences between the upside and downside of airfoils arise in conjunction with the curved airflow. When a fluid follows a curved path, there is a pressure gradient perpendicular to the flow direction with higher pressure on the outside of the curve and lower pressure on the inside. This direct relationship between curved streamlines and pressure differences, sometimes called the streamline curvature theorem, was derived from Newton's second law by Leonhard Euler in 1754:

Where P is the pressure differential, R is the radius of curvature of airflow, ρ is the density and v is the velocity.
My question is that when we apply this formula to calculate specific values for the pressure differential between the top and bottom side of the airfoil, is it right to integrate the right hand side of equation with respect to dR? Given that we are looking for instantaneous pressure differential between two points, and we are given the instantaneous radius of curvature of the airflow (I am aware that this ROC is changing as the air traverses across an asymmetric airfoil).
Thank you for reading!

Yes, but you will neglect viscous effects. And you don't integrate over R, but over the flow path. Also, since v and p are closely related, you first need to add Bernoulli to the mix.

Does this answer your question? How do wings generate lift?

Bernoulli and Newton's third law both derive from the more general conservation of momentum. Please avoid to read anything which try to explain lift saying that you have either to use Newton's third law or you have to use Bernoulli, like if they were two different and contrasting things. This answer gives a very good overview about lift's genesis.


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How to find Radius of Turn given groundspeed and bank angle?
How to find Radius/Rate of Turn given groundspeed and bank angle?
Is GS/bank angle one of the formulas?
What are the formulas needed for Turns Around a Point?
I'm trying to find a way to explain this maneuver as if I was teaching a student pilot?

Groundspeed needs wind information, or you must assume still air.

Good reading in addition of answers: FAA PHAK page 38

Here are some equations - (pay attention how one changes the other - to visualize)
Radius of turn  When speed doubles, radius increases by 4
$$ \text{Radius of turn} = \frac{v^2}{g \times \tan(\theta)} \qquad \text{(standard units)} $$
Rate of turn
If you increase speed, rate is smaller since you make a bigger turn
$$ \text{Rate of turn} = \frac{g \times \tan(\theta)}{v} $$
Hope this helps

The formula for Turn radius is $V^2 / G_R $, where $V$ is velocity (ground speed), and $G_R$ is radial G, which can be determined by taking the tangent of the bank angle multiplied by what G is in the units you are using for velocity (if velocity is ft/sec, then Gs must be in $\text{ft}/\text{s}^2$ ($\sim 32.2 \text{ft}/\text{s}^2$), or $\sim 9.8 \text{m}/\text{s}^2$). This is to ensure the numbers are all in the same scale.
So turn radius is $V^2 / \tan(\theta)$, where $\theta$ is the Bank Angle.
To get turn rate, just think about the velocity, and the circumference of a complete 360 degree circle. The circumference of a circle with radius $R$ is $2\pi R$, and if the velocity is $V$, then how long will it take the airplane to travel that distance? Time is distance divided by velocity. So it will take Time $T = 2\pi R / V$.
And if it takes Time $ 2\pi R / V$ to go 360 degrees, then the turn rate is how many degrees it will change in one second, so that is $360^\circ V / (2\pi R)$.
But $R$ (from turn radius above) is $V^2 / \tan(\theta)$, so turn rate is $ 360^\circ V \tan(\theta) / (2\pi V^2) $, or,
Turn Rate = $ 180^\circ \tan(\theta) / (\pi V) $
NOTE. Again, to use these formulas everything needs to be in the same units: e.g., if V is in $\text{ft}/\text{s}$, then radial G must in $\text{ft}/\text{s}^2$. So in this case, using feet and seconds, you need to add $32 \text{ft}/\text{s}^2$ to the formula for radial G. Instead of $\tan(\theta)$, make it $32\times \tan(\theta)$. If you are entering velocity in knots, then the value of G must be converted to nautical miles per second squared.

In your first sentence, I think you mean TAS instead of ground speed, right? Also, I converted the images to MathJax (Basic Tutorial and Quick Reference).

Depends on whether you want to know the Turn rate and radius in the atmospheric frame of reference (Moving with speed = wind velocity), or rate and radius across the ground.


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How do one "force" VNAV climb mode through a set altitude constraint?
Let's say I'm flying out of EGPH, there is a first altitude constraint at 6000ft automatically set by the FMS. After departure, I will engage my VNAV to climb on profile.
VNAV will hold at 6000ft no matter what I set at or above 6000ft on the MCP.
What is the procedure in that case if ATC clears me above 6000ft to ask VNAV to continue climbing to the newly assigned altitude past the 6000ft constraint?
So far I have pushed LVL CHG and manually set my speed to 250 then 296 to keep the profile.
Any way to do that with VNAV?
Cheers

Pressing ALT INTV will clear the 6,000' constraint and allow VNAV to resume a VNAV Climb immediately -- assuming that

the Cruise altitude is something higher than that, and
the MCP selected altitude is also above 6,000'.

The segment at 6,0000' would be flown in VNAV Path, so the active vertical mode remains VNAV, and ALT INTV is immediately available. When it's pressed, you'd see the 6,000' constraint on the LEGS page go away, and the active vertical mode switches to VNAV Speed, and you're climbing.
As one old head explained it, "ALT INTV is a 'Delete' key."


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Calculate Rudder Angle by Bank Angle
My question: Is rudder angle equal to bank angle? Or, does rudder angle has some relationship with ROT formula?
Below is my steps trying to solve this question.
Step 1: Found below graph from this article showing that vessel's rudder angle (guess it is a close case study) should be in a quadratic equation to the radius like radius = a * rudder_angle^2 + b * rudder_angle + c

Step 2: I check back the ROT equation, ROT (°/sec) = 1091 * tan(bank angle) / speed in knots. Step 1 is somehow make sense to me because it used tan for the angle.
Then, assume all factors are fixed, any suggestion for the next step to prove the relationship or coefficient between rudder angle and bank angle? Thanks.

An aircraft rudder has very little in common with a ship’s rudder.

Once established in a coordinated turn the rudder angle should be zero.

@MichaelHall not really, you need some

@Federico, I’ve never found it necessary to hold any rudder pressure once the adverse yaw from the initial roll has been compensated for.  Heck, half the time I don’t even bother with rudder for that. (laziness from years of flying a jet with yaw damper I guess…)

Bank angle, as in the angle of roll of the vehicle.

All movement of bodies is caused by the physical forces acting upon them. You’ll need to determine the forces first, then inertia, then the movement follows. It is bad practice to combine some equations of different circumstances and vehiccles.

Then, assume all factors are fixed, any suggestion for the next step to prove the relationship or coefficient between rudder angle and bank angle? Thanks.

There is absolutely no relationship or coefficient between rudder angle and bank angle in an aircraft turning. Your understanding of aerodynamics is incorrect and your theory is flawed.
An aircraft rudder is only there to control yaw. The effectiveness of the rudder also can’t be quantified by the rudder angle alone because there are too many variables.
A few of the variables include density of the air, speed of the air, size of the rudder, the moment of the rudder relative to Center of Gravity, the airfoil shape of the rudder, size and shape of trim tabs and aerodynamic horns, etc. I am sure there are many more variables.

Thanks for the direct answer "no relationship or coefficient between rudder angle and bank angle", so that I don't need to stuggle in those angles.

You are mixing two completely different effects here.  With a boat, the rudder is the primary steering control, while with an airplane, the bank angle is the primary driver of a turn, and bank angle is controlled by varying the roll rate with the ailerons.  And naturally, a roll rate of zero is still compatible with banked flight, so we can still be turning even with ailerons and rudder centered.  (The subtle yaw and roll trim effects that comprise the basis of lateral "stability" will be left beyond the scope of this brief answer.)
I won't try to assess the accuracy of the article about boats, but I can tell you that, depending on the airspeed, the bank angle, the shape of the aircraft itself (e.g. high aspect ratio sailplane versus medium aspect ratio light plane versus low aspect ratio jet fighter), and whether or not any thrust asymmetry exists (e.g. p-factor), in a constant-bank angle turn, for optimal "coordination" (yaw centered or slip-skid ball centered), the rudder may be need to be kept significantly deflected toward the inside of the turn, or no significant deflection may be needed.  (Deflection toward the outside of the turn would be unusual, except to compensate for p-factor.)  The rudder required for optimal coordination while actually changing the bank angle (rolling) is another matter; generally the rudder must be deflected toward the descending wingtip, especially with high aspect-ratio aircraft.
But to a very rough first approximation, airplane turning dynamics are all about the bank angle, and the rudder can be considered optional.  Many small, fast, low aspect-ratio radio-controlled model airplanes have no rudder at all, and still are very maneuverable and aerobatic, apart from snap rolls, spins, knife-edge flight, and other such sideslip-based maneuvers.
So no, you can't just combine a formula for boats with a formula for airplanes like this.

Any stuff I should take a look if I want to explore more on the relationship between turning and rudder angle

@PakHoCheung -- you could start by looking at any ASE answers dealing with turn "coordination", "yaw string", "sideforce" etc.   I've written more than a few myself.   I highly recommend John S Denker's "See How It Flies" website too.  Aircraft yaw dynamics are complex,  it's not an easy thing to really understand.  Google an article "Circling the Holighaus way".  But start by understanding the basic relationship between banking and turning.  Many small, fast, low aspect-ratio radio-controlled model airplanes have no rudder at all, and still are very maneuverable and aerobatic.

Thanks for your suggestion. I'm trying to learn more about the numbers used in aircraft, so that I can apply more real case for my work as I'm a programmer to design a simple software. Will look at those books and see if having some numbers I can apply:)

@PakHoCheung -- basically I think unless you have a rather sophisticated computer model of the aerodynamics, you should ignore the rudder, i.e. assume no rudder deflection is needed, just start by figuring out the relationship between bank angle and turn rate, which depends on airspeed.

The dynamics of a turn involve bank angle AND the weathervaning effect of the vertical fin (the rudder has a secondary function) (plus pitch, but we'll leave that part out to keep it simple).
When you bank, the wing's lift vector is tilted, and the lateral force introduced by the tilt drives the aircraft sideways (it sideslips).  Without a weathervaning effect, it would move laterally while remaining pointed in its original direction; just continue sideslipping.  This sideslip happens initially (briefly) when bank is first applied, and is critical for dihedral effect to work for roll stability.
The result of the sideslip is a lateral angle of attack acting on the airplane's vertical profile, resulting from the sideways movement created by the bank, mostly acting on the fin, or more correctly acting on the vertical aerodynamic center, the vertical Neutral Point, of the entire aircraft.  As long as the Neutral Point is aft of the airplane's C of G (what the fin is there to do), there is a positive weathervaning tendency, or positive static stability in yaw.
So the bank makes the plane slew sideways, the fin develops lateral lift in response (after a slight lag to allow dihedral effect to do its thing in the event you didn't actually want to bank), and rotates the body about the yaw axis to reduce the angle of attack on the fin to near zero.
So the airplane banks, starts to slew sideways, but immediately afterward the weathervaning effect of the fin rotates the body in yaw to keep the body aligned into the airstream and the sideways motion is accompanied by a rotation that makes the airplane follow the arc of the turn.
What the rudder does is allow the camber of the vertical fin to be varied by the pilot (being more or less a wing flap that works in both directions), to apply forces beyond the basic weathervaning tendency, when the weathervaning tendency is insufficient.  What makes the weathervaning tendency insufficient is aileron adverse yaw.
So rudder application is used to adjust the camber of the vertical tail, to apply force beyond the basic weathervaning effect, to cancel out the yawing moment created by adverse yaw from the ailerons.  If the ailerons are neutral while banked, little to no rudder is required because there is no adverse yaw.
So for a turn:

Bank creates a lateral thrust component to move the plane sideways.
The vertical fin responds to the sideways movement by continuously weathervaning the body into the lateral airflow created by the bank.  The fin needs to be small enough to allow a slight lag in this reaction to allow dihedral effect to work, where the bank was induced by a bump and the objective is to make the plane return to level flight on its own, but large enough to give a positive weathervaning tendency beyond that when the bank is deliberate.
The rudder allows the camber of the vertical tail to be varied to increase or decrease the weathervaning force, mostly to cancel out the yaw forces induced by the aileron displacement.  The rudder can also be used to take out the small lag in weathervaning effect you normally get when you bank as mentioned previously.  Rudder application is normally roughly in proportion to the up aileron displacement.  Airplanes with rudder interconnect systems, like the Piper Tripacer, mechanically directly gear rudder movement to aileron movement (using bungee springs) and the pilot doesn't need to move the pedals to maintain a coordinated turn - left aileron gives left rudder and right aileron gives right rudder and neutral aileron gives neutral rudder.


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Questions about items on Jepp charts…

On a Jeppesen IFR low enroute chart, there's occasionally a different altitude below/next to the MEA with a "T" next to it. (For example: V16 between GACEB and SHAKY, there's a "2900T" next to the 4500 MEA.) What is this "T" altitude?

Similar to the question above, but on a Jeppesen high enroute chart, there's occasionally a "D" below/next to a given altitude. (For example: Q20 between Fusco and JCT, there's 18000, with "24000D" below it.) What is this "D" altitude?

On a Jeppesen STAR, there are a combination of dashed and solid course lines. (For example: On KDFW's Sasie 6 Arrival, there are several dashed course lines prior to Sasie, after which the course is marked by a solid line.) What is the difference between the dashed and solid lines?

Thanks.

SASIE6 is not an arrival into DFW airport, though it does serve other airports in the DFW area.

I don't have access to Jepp charts, but I do have access to SkyVector and this March 2012 Jepp legend.

1. On a Jeppesen IFR low enroute chart, there's occasionally a different altitude below/next to the MEA with a "T" next to it. (For example: V16 between GACEB and SHAKY, there's a "2900T" next to the 4500 MEA.) What is this "T" altitude?

From page ENROUTE-6 on the Jepp legend:

35— Minimum Obstruction Clearance Altitude (MOCA).

This corresponds with the Government chart which has, on V16 between GACEB and SHAKY, the MEA 4500 above the MOCA *2900.

2. Similar to the question above, but on a Jeppesen high enroute chart, there's occasionally a "D" below/next to a given altitude. (For example: Q20 between FUSCO and JCT, there's 18000, with "24000D" below it.) What is this "D" altitude?

The 2012 Jepp legend does not list what a "D" suffix means on an altitude, but it does say (referring to the above screengrab)

34— GPS MEA.

We can compare to the Government legend:

and we can say with confidence that the "D" suffix lists the MEA for a DME/DME/IRU-equipped aircraft, just as "G" indicates the MEA for a GPS-equipped aircraft.

3. On a Jeppesen STAR, there are a combination of dashed and solid course lines. (For example: On KDFW's Sasie 6 Arrival, there are several dashed course lines prior to Sasie, after which the course is marked by a solid line.) What is the difference between the dashed and solid lines?

From page SID/STAR-4 of the Jepp legend, a thick solid line represents a "common course used by multiple transitions" while a thick dashed line represents a "transition track." This is analogous to the thick black line for common routes and thin black line for transition routes on Government charts.


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Why did the NTSB issue a full report for this accident?
The NTSB issued a full aircraft accident report https://libraryonline.erau.edu/online-full-text/ntsb/aircraft-accident-reports/AAR73-10.pdf for what seems to me to be a small general aviation crash.  What I don’t understand is why it received this full report and not just a brief https://www.ntsb.gov/Pages/brief.aspx?ev_id=66900&key=0 like other such accidents

It's their job to investigate accidents. A better question would be why they don't do it for all crashes.

While at first glance this may seem like a garden variety GA crash, it is not. It has several factors that make it stand out well enough to conduct a full investigation, to find the actual reason for the accident among many possible factors, and thus make it possible to improve processes to avoid such accidents in the future.
Furthermore, the flight was "general aviation business flight", and while I'm not fully familiar with the regulatory basis for  this kind of operations I'm gonna make a bold assumption this would somewhat fall into the category of professional aviation, further emphasizing the need to investigate the accident.
The specific points of interest, separating this accident from a common GA accident would be:

flight being a "general aviation business flight" with two paying customers (my assumption)
loss of all occupants, totalling three deceased
flight conducted under IFR rules
adverse weather condition, especially known icing enroute
the fact that the weather conditions were brought to the attention of the pilot
the plane not having de/anti-icing equipment, and thus no approval for flight into known icing (FIKI)
the approach method being precision approach radar (PAR)

So the severity of the accident, and it being a "business flight" brought it into specific attention in the first place. Commercial/professional aviation has a lot to lose if the utmost standard in safety is not upheld. There were several interesting factors in the accident: poor weather, icing, no FIKI approval, despite of which the pilot set on the journey, PAR approach, which while generally being a safe procedure, can be very laborous to a pilot not well accustomed to it.
It was necessary to filter all the possible reasons and factors to come up with a definitive report on what went wrong, and how to avoid that from happening again.
Further reading on principles of accident investigation can be found in ICAO Annex 13:
https://unitingaviation.com/news/safety/accident-investigation-provisions-of-icao-annex-13/

To me "GA business flight" sounds like it means Part 91 rather than 135 or 121.

Could very well be, meanwhile I've educated myself, and found that "Business aviation is the use of any “general aviation” aircraft for a business purpose. The Federal Aviation Administration defines general aviation as all flights that are not conducted by the military or the scheduled airlines." So regardless of regulatory basis of the flights operated a gabf, they do deserve special attention as there is a professional aspect to such flights.


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Can a company return an aircraft in leasing?
regarding A380 I see that Singapore Airline and AirFrance return 2 and 5 respectively to their lessors, so I would like to know, how the give back operation works? Are there any penalty to pay?
I was wondering if Emirates too can give back its A380.
Thanks in advance

I'm voting to close this question because it's about the legal relationship between Emirates and their leasing company, which to the best of my knowledge is private.

I'm interested to know about how it usually works. Most airliners are leased and I believe that for a given airline size, deals must be pretty similar. Maybe someone with experience in this field have some interesting info ?

Yes there is a penalty to pay if you break the lease contract by returning it before the completion date. Same as a car.  It may be that they simply continue the lease payments to the end of the contract, or the contract may have some kind not-quite-so-bad penalty that was negotiated to sweeten the deal for the airline to get the deal in the first place.
The airline will do a business case and balance the penalty costs of breaking the lease early against the losses of continuing to run their unwanted behemoth to the end of the lease contract and proceed based on the cheaper option.  Even if they have to keep making lease payments to the end of the contract, it still may be worthwhile to return the aircraft and escape from maintenance and insurance costs, if the aircraft was killing them financially, which is what this sort of thing suggests.

Useless knowledge: the airborne counterpart of a behemoth is a Ziz.


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How to measure wind speed in a wind tunnel
I'm currently building a wind tunnel that moves air at hundreds of meters per second. How do I cheaply measure the wind speed?

What are your budget and accuracy requirements?  There are lots of metrics that can be cheap (pitot tube, anemometer, PIV), but it really depends on what you intend to do with the tunnel.

If you have the ability to make air move at "hundreds of meters per second" an anemometer shouldn't be a problem.

A simple pitot tube attached to a fluid level balance can do this, if you can develop a pressure differential vs airspeed reference for it.

An anemometer will work, but do not place it downstream of any turbulence-producing object, or you may destroy it.  Speaking from experience.

An anemometer was good enough for the Wright wind tunnel.


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Does anything prevent an airline from claiming that a flight cancellation was due to weather, when it was actually for another reason?
American Airlines has a policy that if a flight is cancelled for any reason other than weather, AA will pay for stranded passengers' hotel and meals until the passengers' rebooked flight. If the cancellation is due to weather, passengers must pay for their own lodging and food.
This seems to create an incentive for the airline to blame suboptimal-but-still-flyable weather conditions when they must actually cancel a flight for another reason. There is a lot of news lately about cancelled flights due to crew shortages and pilot strikes. It seems in an airline's financial interest to shift the costs associated with these cancellations (e.g. unexpected hotel stays) onto passengers.
Are there accountability mechanisms to prevent an airline from doing this? If so, how do they work?

AA, or any other airline, does not operate in a vacuum.
"Hey, we had to cancel FLT 102 from Pittsburgh due to weather."
The rest of the world...'Hey, wait a minnit. Delta, United, FEDEX all took off and landed within 5-10 minutes before and after. So...'
They are in the business of getting people from A to B. Not necessarily screwing them over in doing so.

If you wanted to make a case against an airline you might contact ATC at both ends of the flight and ask about weather conditions.  If both say that they are able to operate then there’s grounds for a ‘please explain’ from the airline.

Every company is in the business of maximizing revenues and minimizing expenses. If that means lying to avoid paying for 200+ hotel rooms, so be it.

Maybe out of 200 passengers, only ~10% will complain that weather is not a probable cancellation cause. Those 10% might get hotels & meals. The other 90% are still good savings. (btw this thread would better fit "Travel")

In the history of commercial air, have we seen any documented instances of this? If so, was there any blowback to the airline?


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Why do flights approaching Kabul seem to take a different route since the Taliban took over?
From a reporter on Twitter:

Nerdy question but genuinely curious:
All fights into Kabul would previously approach from the east, flying towards the direction of Nangarhar, then making a U-turn over the Surobi basin, then descending westwards into Kabul. Now they seem to all approach via Logar, meaning they descend south of Kabul,then making a smaller left-turn into the airport. It's much faster that way of course so that's great (Herat-Kabul flight time was 45 mins only compared to over 1h before).
Any particular reason for the switch in flight path? V curious!

Source: @stephglinski

The question you are better off asking is why is that happening since the coalition forces pulled out.

Not familiar with the area, but perhpas certain parts of the airspace were permanently reserved for military operations before the US left. Now that those operations came to an end, there is more airspace available for optimising routing.

"All flights" suggest the new government has changed the approach procedures for the airport.


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Can you get a medical certificate with degraded vision?
I am blind in one eye and have a -11.25 prescription in the other, correcting to 20/40. I am afraid to go for a medical and fail, since I was told I couldnt challenge that if I did.

What country/jurisdiction are you asking about?

No one but your AME is qualified to speak to your specific medical conditions. However, the FAA medical standards are available online and you can compare the standards to your vision prescription.
In general it is possible to "challenge" a non-issued medical, which is called a "deferral," and receive a special-issuance medical certificate. But this can come at a great cost in terms of both time and money.
The recommendation I have seen is to set up a consultation, not a medical exam, with an AME. You should be very clear with them that you are not trying to have them make a determination on your suitability for a medical certificate, but rather you are requesting an examination to see if they would have any problems issuing a medical certificate if you were to actually apply for one in the future.

If you have a valid US driver's license and have never been denied a medical certificate, you can also look into the Sport Pilot certificate, which has greatly reduced medical hurdles. This certificate affords you very limited flying privileges, but is worth investigating if you are concerned you would not be able to receive a standard medical certificate.

Near as I know, being blind in one eye is not considered a disqualifying medical condition. You can read a list of disqualifying medical conditions here.  You can also read about FAA aeromedical dispositions regarding eyes here.
Other than that, per §67.103, §67.203, and §67.303, the only requirements for current myopia is that your vision be correctable to 20/40 or better and near vision correctable to 20/40 or better.
Another excellent resource is the Aircraft Owners and Pilots Association (AOPA) medical resources site.  They had this helpful piece of information on monocular vision.


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What makes an engine suitable for supersonic flight?
I would like to know for example if someone can take the "core" of an CFM56 used on A320, redesign it by adding a supersonic intake, a convergent-divergent nozzle, and reduce its bypass ratio, but keeping the same stages of compression and turbine stages. Will it be able to achieve supersonic speeds?

Yes.
This is more or less exactly what had been planned for the (now defunct) Aerion supersonic business jet.  The engine was to be developed by GE, with the core of a CFM56, the fan replaced with a lower bypass fan, inlet and exhaust replaced, and that's it.  The core was to be off the shelf CFM56 core.
Also, the F101 and F110 fighter jet engines and the CFM56 share a very similar core.  It's not exactly the same, but it's fairly close.

Wait a minute. The linked answer from @ymb1 states that the CFM56 was actually derived from the GE F101 core, with improvements fed back into the F110.

To complete this answer: the idea is simply that you do not want a supersonic flow over the compressor blades. And the inlet has to slow the flow enough that the compressor won't become supersonic.


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Which would be the best placement of an engine for a supersonic buisness jet that has an intake of 2-D ramp?
I would also like to know if possible which would be the advantage/disadvantage of placing the engine under or over the wing for example.

Over the actual wing, sorry for not specifying.

The linked adressed helped, thank you very much!


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Thrust varaition of a Turbofan engine with altitude and mach number
my classmates and I are trying to find a mathematical model for a low bypass turbofan engine, we ended up finding a model given by Snorri on "General Aviation Aircraft Design", but the behaviour of the graph is totally different to the ones given by engine manufacturers. What we want to achieve is the behaviour of a low bypass turbofan engine from sea level at Mach 0 to an altitude of 15000 meters and Mach 2.1. The first graph is taken from Snorri, while the second graph is from other textbook. I would like to know why they have such a different behaviour, thanks!
*

Did you notice the first graph is not thrust, but thrust ratio? Is it intentional?

Yes, I did notice. What I was wondering is that it gets values bigger than 1, so that means that the thrust is bigger at certain mach numbers when keeping the same altitude. While the second graph never increases the thrust more than the sea level at Mach 0.

When the plane picks up speed there is more airflow through the engine, function on inlet shape etc. Hence my question about a reference of the setup of the 2nd graph.

The graphs have different vertical axes and units. The first one plots Thrust@Altitude/Thrust@SeaLevel on the vertical scale, which is dimensionless. The different lines depict this ratio at different altitudes.
The 2nd graph plots thrust in pounds. Period. (And gives a value for Specific Fuel Consumption). Different graphs for different altitudes. In order to convert into a graph like the first one, all values at altitude need to be divided by the corresponding value at Sea Level.

What we want to achieve is the behaviour of a low bypass turbofan engine from sea level at Mach 0 to an altitude of 15000 meters and Mach 2.1

Easiest done with the 2nd graph type, since you need the following steps:

Determine required thrust @ TakeOff, climb, cruise
Make a time scale of Mach, altitude, thrust. So at each time interval, determine these 3 values.
Look up the maximum available thrust in the graph - throttle setting is a variable as well.

There is no further information on what the circumstances are of the measurements in the 2nd graph. Is it engine only in a ground based test stand, or aeroplane mounted data in flight? A reference would be useful.


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Do wings actually flex upon landing (especially hard landings)?
I have been playing some flight sims and have noticed that in some of them you get wing flex during hard landings. Is it realistic? Can wings flex upon a hard landing?

Wings flex during all phases of flight.

Not just in flight, on the ground as well. Taxing, you can see the wingtip flex up and down a couple of cm.

One thing you learn in engineering is that everything is a spring, and everything flexes to different degrees.

It appears they do!

So does your car's chassis. You don't get to build any transportation vehicle without studying this at length, and designing your vehicle so all normal flexure happens in the elastic range (bouncing back), and not the plastic range (de-forming) for that metal and thickness.  If you want to see "plastic" forces, watch Dukes of Hazzard.  Most of those Dodge Chargers did not survive those jumps.

Fun fact: if you are seated in the right place, you can observe this from inside the plane.  Which can be a little unnerving.

It's even cooler when the floor starts moving up and down like an articulated bus. If everything didn't flex, all of it would break.

Also looking down long corridors on ships during heavy seas.

Can see wing flex midair during the somewhat viral video storm Eunice at Heathrow airport from friday too - it certainly happens at all phases during flight.

They flex when parked on the ground.

Yes, when the wheels touch down the wings still have a negative vertical velocity component and they sag down dynamically, and then rebound back up again to a constant value of "static" sag that reflects the weight of the wing and its stiffness.
In the C-5 heavy transport, the touchdown sag  was sufficient to "eat up" the fatigue design margin in the huge wing attachment structure which transferred wing lift to the fuselage, causing premature cracking. This required a significant redesign and retrofit work on that "box structure" to allow the C-5 airframe to meet its design lifetime goals.
At one point, the Air Force considered using active thrust vectoring from the engines to "prop up" the wing during landings and thereby reduce the magnitude of flexure. One of my engineering professors worked on a dynamic model of C-5 wing flexure stresses and strains during touchdown sag to see if tipping the engine exhaust stream downwards was a viable solution to the problem.

Is there any good video of this happening? I feel like a video would say 1000 words.

@stevec, not that I know of. -nn

Not sure if it's the best example, but here's one: https://www.youtube.com/watch?v=OkL5tFmk9BU

Was there a solution??

Yup. While flying, the wings are supporting the aircraft's full weight. After touchdown this weight transfers to the wheels, preferably smoothly and rapidly. So of course the wings will flex.
However some flight sim designers turn this effect up to 11 ;)

I remember playing X-Plane 11. I don't know if it was me settings (probably) or what, but when the plane got high enough, this would happen to the point it would flap its wings similar to a bird. I could never figure out why but enjoy the game.

It's up to the modeller in X-Plane - you can scale it down with some keyhole surgery to the aircraft's .obj files.

Are you talking about bouncing up and down or "remaining sagged"?
For the first one, oftentimes upon (hard) touchdowns, there is some bouncing.
For the second one, the wings remain "sagged" while producing lift.
If there is still noticeable airspeed, the wing will still be producing lift, so there will be some "sagging" indeed.
BUT as soon as the spoilers are activated, (most) lift gets spoiled and the wings stop flexing.
It's actually very cool to see how the wings drop as soon as the spoilers are deployed.

Sagging is usually downward. Wings flex up while providing lift. They sag or “droop”  under their own weight when not providing lift.  A B-52’s wings can flex upward by as much as as 22 feet and droop 11 feet on the ramp. They even have outrigger gear near the wing tips to keep them from hitting the ground.

Please don't use codeblocks for anything that is not actual code.

The sag of the wings is particularly apparent, if you sit in a window seat near the wings.
The following pictures were taken from the lower deck of an A-380 in-flight  during the approach and later post-flight on the ground.
Notive, that in-flight, the root of the wing-tip is visible, while post-flight, only a portion of the wing-tip can be seen.

Structures like aircraft wings and even bridges are quite rigid, but not totally. There is always some strain in response to stress (stretching in tension or compressing in, well, compression). Bending loads are basically just tension on one side and compression on the other, so bending loads result in, well, bending. Structures that are extremely rigid are often brittle - in other words, they tend to fracture before exhibiting much, if any strain. The visible flexing of an aircraft wing is generally a good thing, because it is a more forgiving response to high levels of stress than a sudden brittle fracture. The only downside to a lot of flex is the possibility of harmonic resonance, in which oscillations can build up in intensity and overload the structure (in wings, it is known as flutter). Aircraft wings are designed to allow for some flex to provide a forgiving response to high stresses, while remaining stiff enough to avoid flutter.
On a hard landing, the wing unload its lift abruptly, so the upward flex it had under flight loads is suddenly relieved, but the vertical velocity of the aircraft is suddenly arrested by the landing gear as it contacts the runway; the wings do have mass, and thus inertia, so want to keep moving downward even as the rest of the aircraft's vertical velocity is canceled by touchdown. Put all that together, and the wings will always appear to flex downward on landing, it's just more pronounced on a hard landing.

If you get many chances to fly on an airliner, sometimes sit behind the wings, and enjoy looking out the window, you will quickly learn that the wings flex all the time. They are long and fairly thin, and all materials have some give. During turbulence the flexing can be quite visible. I think you can see it during landings too.


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Kinetic energy to perforate skin/fuselage of aircraft
I know that most aircraft have skins that are either aluminum or an aluminum alloy variant. I'm trying to figure out the minimal amount of kinetic energy that would be required for a projectile to penetrate/perforate an aircraft.
Does anyone knows of any useful papers about this? Or, perhaps, can anyone offer useful guidance or advice?

It depends on the size of the projectile. A standard 9mm pistol bullet (~400-500J) is definitely considered unsafe if fired inside a pressurized airplane. Some purposed-built pistols for onboard security agents has a muzzle energy as low as 60J (Chinese type 84 pistol).

I have a pellet rifle that can shoot through a couple steel cans, so it isn’t a lot…. How exact of an answer are you looking for?

Size  and shape. One innovative design for tank projectiles was a very skinny high density  dart shaped projectile with fins at the back, without any explosive at all. By reducing the cross sectional area of the projectile, not only did it reduce drag enormously, it also allowed the kinetic energy to be applied to a much smaller area of the impact surface, so the energy per square inch at the point of impact was significantly higher.

Thank you, @user3528438.

@Michael Hall, I'm not looking for an EXTREMELY accurate answer. I'm just wondering if there is any officially documented article or paper that provides an estimate for the limiting kinetic energy that can potentially cause damage to the skin of an aircraft.

But are you looking for a mathematical formula, or a practical answer?  Other than e=mv squared I can't really help you with the math, but as Charles pointed out the size and shape matters -  You could probably fling a common dart at a Cessna and make it stick, but does that help you?  Context is needed to make any answer useful or interesting.

@MichaelHall, a practical answer.

If my dart or pellet gun example is good enough then I would be happy to expand that into an answer.

Transport airplane use "damage tolerant" structural design which means redundant load paths within a structure. This is mainly to provide a safety factor in the face of metal fatigue, but it also means tolerance to physical damage (like bird strikes).  If you were firing .50 cal bullets at an airliner from a WW2 fighter, you'd have to chew up a key stress zone with quite a few bullet holes to fatally compromise the structure.  Damage that causes stress concentrations that induce cracks over an extended period is one thing, but damage to make it break on the spot is another entirely.

Only a few joules.
This isn't about energy. One could perforate an aircraft's skin with a millimeter-thick punch.
The theoretical deformation energy of 1 mm^3 of metal is UTS*elongation*volume. For 7475 aluminum (one of the strongest alloys used in aircraft), that comes to 0.53e9*0.12*1e-9 = 0.06 J/mm^3. This amount of energy can be slowly delivered even by hand, e.g. with a hand drill.
For a projectile, you'll need to use an armor penetration equation. The Lambert-Zukas formula is the most suitable here.
Plugging the values into the online calculator, a 10*10 mm, 10 gram projectile can penetrate 1 mm of aluminum at 40 m/s. That's an energy of just 8 joules. 1 mm is about the thinnest an airliner's skin can be at any point, usually only in the crown. Most are thicker, and GA aircraft can have skin as thin as 0.5 mm.
To penetrate 1/8" of aluminum, the high end of the range for airliner skin thickness in passenger areas, the same projectile would need 118 m/s. That's an energy of 70 joules.
Energy requirements will scale roughly linear with reducing or increasing the hole's diameter, with 7 J for 1 mm, 35 J for 5 mm.
Note that a 10mm hole will not compromise the aircraft's integrity, airworthiness, or anything else. It will only make a small amount of noise.
Airliners aren't airtight: there is already a much larger hole in the fuselage. They take fresh air in from the engines and dump used air through the outflow valve.

What matters for damage is the size of the hole. Blowing out a window will generally cause some winds in the cabin. It's dangerous to the passengers and there was one case when a blown window caused a fatality, to specifically the passenger next to it.
Some amount of damage will cause worse effects. This amount is unclear and depends on the aircraft. At low altitudes, pressurization isn't necessary, so one can fly open-cabin all the way. As an extreme example, this airplane actually landed.

But most of the time, an aircraft with this amount of damage would not end up landing safely. There was some luck involved. The area torn off was the crown, which doesn't carry much load - the thick and heavy lower fuselage between the wings and the cockpit held it together.
The threshold hole size to risk the entire aircraft is somewhere between these points. Unless it hits something critical.

this is getting more confusing the further I go. What, then, would compromise an aircraft's integrity or airworthiness.

@HannahSanders, that's because there isn't an easy answer.  People pierce their ears and other parts all the time with no ill effect, but shove that same spike through your aorta or frontal lobe and you will have trouble.  Airplanes are kinda the same way...  If a bullet punctures the skin of the wing it may be no big deal, but if it severs a hydraulic line, control cable, or fuel tank it would be a problem.  Help us understand the root issue and you might get a better answer.

@HannahSanders Overall, simple skin punctures punctures aren't a danger in terms of completing the flight. Large holes may overcome the pressurization system's capabilities, but the plane can fly lower to compensate. If there's not enough fuel, the pilots still have enough emergency oxygen to carry on at an intermediate altitude, even if everyone else will get incapacitated.

You won't be able to punch a hole in a .040" to .063" thick 2024 T3 skin (typical for fuselages - 7 series alloys are typically used for wing planks) with a hand punch unless you are able to drive it with a fairly hefty hammer.

@JohnK True, though mostly because it's thick and dull - the energy is there. I'll edit to clarify.


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Why was the second runway at Sea-Tac Airport built so close to the first?
The second runway (the eastern 16L/34R) was built 800ft. to the east of the original runway 16C.
Almost immediately it was criticised as being unusable for simultaneous operations unless using VFR rules... up to 44% of the time according to some news articles.
Why wasn't it constructed with greater separation?

TL;DR/Abstract - Political, financial, and social expedience are often the dominant forces in the development of infrastructure projects - Sea-Tac is no exception.
The history of Sea-Tac is messy, as airports in urban areas always are.  The short version of the answer is that it's a combination of sociotechnological-lock in, prohibitive construction costs, NIMBY/BANANAism.
For more in-depth blow by blow of the third runway expansion I'll point you to this article on the subject, excerpted below.
NIMBY/BANANA
Most people are familiar with NIMBY (Not In My BackYard). That force has only gotten stronger since the 60s/70s when the term became popularized.  The planning field has begun to use BANANA instead: "Build Absolutely Nothing Anywhere Near Anything."
Stuff like airports get built as far from population centers as is economically feasible, and as close to them as is politically feasible. In Sea-Tac's case, they had political tailwinds: World War II

On March 7, 1942, three months after Japan attacked Pearl Harbor, the Port of Seattle undertook development of Seattle-Tacoma International Airport at the urging of the federal government. A new airport was desperately needed to help relieve pressure on Seattle’s Boeing Field and Tacoma’s McChord Field, which were commandeered for warplane production and military use in World War II. After rejecting a site on the Sammamish Plateau as unsafe, the Port chose a sparsely populated plateau near Bow Lake, roughly midway between Seattle and Tacoma.

The 2nd runway went in as part of the '67-'73 airport expansion, and at that point you've got a question of where to put the thing.  Note that they decided to put it between the terminal and the existing runway. We can look to the history of the third runway for our answer of why:
The third runway (Now 34L/16R), which was explicitly constructed to compensate for the weaknesses of 16L/34R, required (emphasis added):

...the westward extension of the airport plateau atop some 17 million cubic yards of fill dirt, ... The Draft EIS identified the need to acquire about 400 homes and cited potential effects on nearby creeks and wetlands.

The third runway required legal action all the way up to the Supreme Court of the State of Washington - a $15M, 10 year legal effort on the part of the project.
By comparison, runway 34R/16L was built essentially within the existing boundaries of the airport, which requires almost no permissions or permitting whatsoever.
SOCIOTECHNOLOGICAL LOCK-IN
Mild disclaimer: my doctoral dissertation work focused mostly on energy policy, so I'm extrapolating a little bit here to the transport sector, but given the history of runway 34C, I'd bet money I've got the right of it.
One of the more pernicious forces against change is the presumption of expertise given to experience. "This person's been doing this for forty years," is often viewed as a reason to trust the judgement of a person. Not entirely without reason, mind you, but when technology is advancing rapidly (as was aviation in the 60s/70s), you can run into difficulty where the person who's been building airports for forty years (since the dawn of aviation at that point) "knows" how they should be built and what minimum distances you need.
The issue is that most of that experience is in building airfields for piston-driven stuff like the DC-3 and DC-6.  Jet aircraft were rapidly taking over the fleet, and whoever Sea-Tac was allowing to make decisions about runways was demonstrably behind the technological curve: the main runway (34C) had to be repeatedly lengthened as each successive assumption about how long the runway would need to be proved incorrect - and this is in Boeing's backyard. We see this effect time and again in sector after sector from city planning, to medicine, to electrical power: "This is how it's always been done" is an incredibly powerful rhetorical tool.
So at the time, 800ft. lateral separation was probably billed as "plenty." After all, the newfangled jets were expensive, how much of the air transportation sector could they possibly come to claim? 34R/16L was longer than the 1st runway by far, and so presumably was there for the 'rare occasion' when you'd need to land something big.
CONSTRUCTION COSTS
Ultimately, Sea-Tac had to build the third runway, which involved titanic landscaping, protracted legal battles, and 1.2 billion, with a B, dollars. It also involved several eminent domain actions, and a mountain of environmental impact abatement. Anyone still on the fence in the face of the two forces above can be nudged off by the comparative price tags of the projects.

Excellent answer!  I grew up on the Sammamish plateau and never heard it was considered.  (Before my time, but still local history). I might suggest moving the TLDR section to the front as an abstract.

NIMBY I knew. #TIL BANANA. That alone was worth reading the answer, the rest was bonus! ;)

@FreeMan We also toss "NOPE" around. Not On Planet Earth. I literally learned these as part of my transportation planning classes.

The curious question in all this is why they didn't follow on 16L/34R very shortly after by closing the original 16/34 and rebuilding it further west. That would seem to have bought them many years in which they would have been able to support parallel operations, before traffic grew to utterly require them.

@PhilMiller Because ANY expansion of the airport grounds triggers a huge amount of work, it's very common for change, when it does come, to be as minimal as possible in that specific moment.  Honestly that a third runway exists at all is something of a miracle.

I was kinda figuring that there was some room to the west of the original runway already within the existing airport boundaries, and perhaps with enough margin around it. Just not nearly enough for where the third ended up

It's interesting how difficult it is to look up -anything- about the 2nd Runway. 1st Runway? Yep. 3rd Runway. A mountain of info. But for whatever reason, there just wasn't that much 'press' (or at least not much one can easily find.)

@jchwebdev That's one of the reasons I conclude they didn't need any real permitting or review process... if they had, NIMBYism would've seen to it that it hit the papers.

If you want an interesting discussion on the reverse logic, look into the development of Denver International Airport. After years of fighting NIMBYs over growth, noise, etc. at Stapleton, the city procured a huge chunk of land (it's the largest airport property in the US) and proposed building DIA on the site. The site is so big that NIMBYs aren't an issue. So the opposition was; it's too expensive, it's too far away (~17 freeway miles past Stapleton), and a few other things. Obviously, it was built and it's pretty awesome, but even doing the right thing is a challenge politically.

@Gerry In my limited experience as a planning intern, doing the right thing is even harder.

I think NIMBYism is why the nearby Renton airport runway is so short. It extends to the edge of Lake Washington. Boeing has a plant there that has built every 707, 727, 757, even most 737s were built here, took off down the 5,382' runway and never returned. It's too short for those planes to land. If problems develop, they land at another airport.


text:
Using a Foreign-based FAA license while getting permanent license
I am an American Expat who got my EASA PPL(A) license while living abroad.  I am about to move back to the US and looking into a permanent conversion to an FAA license.
Per I have a European EASA license - what do I need to do to be allowed to fly in the US?
 the best option seems to be re-taking the FAA tests.  Otherwise I would have to find an EASA examiner in the US to avoid my EASA license expiring (perhaps thats not as hard as I assume?).
My question is am I allowed to file/use for the foreign-based license while training for the full license?


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Hypothetical Ramjet-Scramjet-Rocket Combination?
Theoretically, could a ramjet-scramjet-rocket combination exist that operations like a rocket for taking off(below operations speeds from the ramjet or scramjet) or in space, and then switch to ramjet/scramjet mode when accelerating up to orbital velocities?

This is called a "combined cycle" engine and has been studied a lot, maybe flown a few times on experimental basis:

The RBCC, or rocket-based combined cycle propulsion system, was one of the two types of propulsion systems that may have been tested in the Boeing X-43 experimental aircraft. The RBCC, or strutjet as it is sometimes called, is a combination propulsion system that consists of a ramjet, scramjet, and ducted rocket, where all three systems use a shared flow path.

Source: Wikipedia article and its sources


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Flow Straightener location
Do wind tunnels with flow straightener after the flow contractors have slower flow velocity compared to a wind tunnel with the flow straightener right after the fan? Note: I'm assuming the same fan is being used.


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Why Apollo 11 was launched in summer? (Performance question)
The question could seems stupid, but i think that best moment to launch a rocket is when temperature is lowest in order to achieve the best performance in a reaction engine. I do not know if there is some explanation to this or is just because that performance degradation is irrelebant.
Thank you for your time.

Duplicate of Effects of atmospheric conditions on rocket performance?.

I would think that summer would be the best time to launch as warmer temperatures mean less dense air and less drag.

Welcome to aviation.SE! I think you'll get a better answer on space. SE. There may be many reasons why Apollo 11 launched when it did, including political ones.

The temperature of the environment doesn't have a significant impact on the performance of a rocket engine. Air breathing engines have better performance in cold air because the mass density is higher at a given pressure, which allows them to ingest more air, and because the thermodynamic efficiency of a heat engine increases when the temperature of the cold side decreases.
A rocket uses oxidizer from a tank, and the thermodynamic cold side temperature is the temperature of the propellant before it gets burned. Thus, atmospheric temperature doesn't change rocket performance like it does for air breathing engines.
Remember that rockets aren't pushing against the air, they're pushing against their own exhaust. Atmospheric pressure slows down the escape of the exhaust, reducing thrust. Rockets will produce more thrust in a vacuum than they will in the atmosphere.
The main concern for timing the launch of Apollo 11 was making it happen as soon as possible, both to beat President Kennedy's promise to land a person on the moon before the end of the decade, and to beat the USSR to the moon.


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Why is VHF still used?
I have a rather easy(?) question. Why is VHF radio still the main communication method between the ATC and pilot?
Is it because there is no better solution at the moment?
Best regards

"If it isn't broke, don't fix it"

Just to note VHF is simply a frequency band - it can, and does, contain digital data. Additionally, UHF is also used for aviation purposes. I presume you're asking why aviation used AM radio, rather than VHF specifically

The reason radios in general are used is covered in this question Why is radio communication still used?
As for why VHF is the band of choice its largely because its assigned for aviation use and the the radio spectrum is not unlimited. Here in the US the FCC regulates which bands are for what, you can find the full list here and you will see that many of them are in use for lots of different things so using a higher (or lower) band for aviation may not be possible as they are likely used for something else.


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Is there a standard button layout on a side-stick for software-based flight simulators that matches what would find in real life?
My son wants to become a pilot so we started him off with the FlightGear Simulator and a joystick with lots of buttons so he can get his feet wet.
Is there a standard layout for buttons on a joystick that would more-or-less match what you would find on commercial side-stick aircraft?  If there is then I would like to configure them so it meets what he might find in the real world.
Here is what we have setup:

normal pitch/yaw/roll for push/tilt/twist
hat button for elevator/aileron trim
lever for throttle

But what about the many other buttons, how would they (approximately) map to a commercial aircraft stick?

Commercial aircraft side sticks usually don't have that many buttons. Usually a PTT, AP Disconnect and maybe a priority button.

Thrustmaster sell an Airbus "inspired" joystick which is pretty much as close as you'll get to a replica for home simulations.

That’s probably the least of your concerns.  A pilot can adapt to a new button placement in a few minutes.

I think many of the desktop flight sim joysticks are inspired by military jet HOTAS (hands on throttle and stick) controls, which have far more buttons on the stick compared to commercial aircraft.

There are quite a number of questions here about using a home flight sim as training for flying a real aircraft, including the benefits and hazards. I don't know how old your son is, but you may want to investigate these other questions before trying to build him a "real" home-based flight sim.

As mentioned, real life side sticks are very simplistic compared to gaming devices. There is basically an autopilot disconnect push button and radio tangent (aka push-to-talk) switch. On aircraft that require manual trimming there is also the elevator trim switch.
But there is also another aspect in cockpit design that can be adapted to gaming. Critical flight controls are positioned in a way that they can be easily reached quickly and reliably. Also one thing that is crucial in real life that is hard to simulate is maintaining good outside monitoring.
Assuming your son is right-handed, I would put the view controls to the hat switch to enable quick look-around and elevator trim to the left side top buttons. On the right side top buttons I would recommend flaps up and down. Those controls are crucial for maintaining safe flight path during takeoff and landing. The trigger I would use as a wheel brakes, again to keep hands on controls during the landing run. Alternatively trigger can be used as push-to-talk switch like in real life Airbuses if your son wants to fly online. On the base you can add other frequently used controls like landing gear etc.
As Jim mentioned in the comments, trying to simulate realistic cockpit environment in home is the least of issues. Of course, there are lots of additional hardware you can buy if your son really gets into simulator flying. You can also sacrifice your garage to build full size replica of a real airliner cockpit as some people have done. That should be a fun father-son weekend activity :)
There was a significant transition in flight training a decade ago when suddenly model aircraft hobbyists were replaced by simulator flyers as rookie flight students. That raised a set of whole new issues as people had learned a lot of "bad habits" that had to be unlearned. Biggest of them were mismanagement of their focus (like reading a map in traffic circuit), not maintaining a good lookout while flying (ie. constantly flying head down scanning the panel) and not trimming the aircraft. Then again some avid online flyers are already very fluent with their radio communications. The simulators are realistic enough to simulate real life flying in bad or good. Also in theorical training there is sometimes lots of resistance to re-learn things as self-educated sim flyers have gained their knowledge without reference to the real world. Some of their information is irrelevant, misplaced and often misunderstood.
All that being said, simulator flying is a great hobby and awesome entry to the aviation community. As a professional pilot, ex-simmer and father myself, I think it is great that you are involved and encourage your son to keep that spark of dream alive. Your son should participate in the online community and fly online with other simmers. That way he can ask questions and keep learning about his new interest.

It really doesn't matter.
It doesn't matter as there is no such thing as "standard buttons" on a side stick or control column. Take for example the A320 that has a priority take over button which sounds kind of useless to your scenario. Another example is the control column of 737(-800) that has 2 switches used for electrical trim. Such a switch doesn't exist in an A320 as the computers trim an Airbus A320. Finally, the most "standard" button (and perhaps the only one) on a control column is the communications button. But if one flies alone (ie not on a network with other players) to practice let's say a traffic pattern, that button is also useless -there is no one to transmit to.
Last but not least, the very important thing that other answers are missing to mention is that the rudder control is separately on pedals and not on a the "twist" control of a joystick1. That by itself can lead to some frustration when trying to line up the aircraft. Related anecdotal story: this week I was at Madrid World ATM Congress. There I had the chance to try an LPV approach driving an A320 on X-Plane2 (11 I think) with a VR headset with the exact same joystick that you have at the picture. At some point I looked momentarily down and I realized that I was inadvertently fiddling with the rudder (the pedals were moving a lot) more than I wanted to fiddle with -which was none at all. Apparently I was using the twist as I was trying to roll. Moral of the story is that there is more than meets the eye on a joystick than "getting the button setup right".
In my opinion3, a child aspiring to become a pilot needs to learn at least the notion of good airmanship. According to Skybrary,

Airmanship is the consistent use of good judgment and well-developed skills to accomplish flight objectives. This consistency is founded on a cornerstone of uncompromising flight discipline and is developed through systematic skill acquisition and proficiency. A high state of situational awareness completes the airmanship picture and is obtained through knowledge of one’s self, aircraft, environment, team and risk."

Confidence (not arrogance), situation awareness, orientation skills, stress management and sure why not some training on the simulator will help better. And the joystick comes last. Like any other hardware on a Personal Computer, one can set it up as it's more convenient to the individual.
A huge caveat on this last sentence though: no matter what, please don't inverse some fundamental actions as this might impose bad habits. To pull the nose up, joystick moves towards us, to dive it's away from us -obviously. Flight Gear must have it like that by default, but if that's not the case for any reason, change it promptly. I am mentioning this as I remember a user writing in a comment here in AVSE that some games lately have reversed the up and down keys. I can't find the comment unfortunately.

1 By all means I am not trying to convince you to buy yet another piece of hardware. Building a home cockpit can become a dangerous rabbit hole.
2 I am not affiliated by any means with X-Plane.
3 I'm neither a father nor a pilot so my opinion might not really matter.

+1 for separate pedals. Flying a helicopter with the joystick 3rd axis is quickly boring, as well as flying with "autocoordinated turns" for GA aircraft.

Aircraft rarely have more than two or three buttons on their yokes. Joysticks like the one pictured are intended more for fighter-type games, where you have to quickly fire the gun, select missiles, designate a target, etc., all while maneuvering the plane. Civilian aviation just isn't that fast-paced, so there isn't any point to covering the yoke in buttons.
There's no standard for buttons on the yoke, even for the few buttons there are. Not to mention that the yoke can be customized by the plane's owner, so if I really wanted, say, a transponder on/off switch on my plane's yoke, I could have one.*
But to actually answer the question, by far the most common control on a yoke is the push-to-talk button, which is almost always operated by the index finger. Note that this is not the same as the trigger; the PTT is usually up higher on the yoke than the place where the finger normally rests, to prevent accidental activation. But most computer joysticks don't have a button in that position at all, so the trigger will be the closest alternative.
For planes with an autopilot (which is essentially all commercial planes), there will often be an autopilot disconnect button on the yoke. Similarly, there may be an autothrottle disconnect button on the throttle. Though this is rarer, I've seen turbine-powered planes with the starter and/or fuel disconnect on the yoke. But those can be located in different places even within different planes of the same model, so if you're going to assign those functions at all, just pick a button.
*I realized just before posting this that a non-aviator might not understand how ridiculous this is, so let me clarify that this is the most ridiculous example of a control to have on a yoke I could think of. Just about the only reason you'd need to turn off your transponder in normal conditions is if you're flying in formation and aren't the lead plane.


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What does "closed traffic" mean?
I'm a Japanese ATC working in Japan.
I want to ask about "closed traffic". I checked 7110.65 for this.
Question 1: What is successive operation?
One day I was on duty and the air force pilot said "Request right closed" each time after completing a touch and go.
Question 2: Does a USA pilot use "right closed" to mean "right downwind" when they want to turn closewind?
By the way Japanese pilots usually use "Request right downwind" (for T/G, etc.) each time when they remain in traffic pattern.
I control Japanese and USA aircraft ... it's too difficult to learn 7110.65.

In that case I would imagine that he was requesting a single loop in the pattern (and then either a full stop or to depart the area). But I am not sure! So the best thing to do is ask for clarification: "Air Force 12345, confirm you are requesting one time around and then full stop?" or "Air Force 12345, confirm you are requesting multiple operations in the pattern?" (Or you can just clear him for a T/G every time and wait for him to request something else.)

Thank you Mr.randmhead!

The most important thing is Ask for clarification. I think so too.Not only in this situation, it is dangerous to let it run when it is unknown.My boss got angry at me,when I was training at TWR.

There are two meanings, one for civilian pilots and one for military.
Civilian
As an FAA controller, I was taught that "closed traffic" means "successive operations," which is in line with the Pilot/Controller Glossary:

CLOSED TRAFFIC- Successive operations involving takeoffs and landings or low approaches where the aircraft does not exit the traffic pattern.

This means the pilot will remain in the local traffic pattern (and furthermore, specifically in the left or right traffic pattern as assigned by ATC) for multiple operations (touch and goes, etc) in a row. (This includes the downwind, as you mention, but also the crosswind, base, and final of course.) The pilot does not need to ask for permission to stay in the traffic pattern each time they depart, and ATC does not need to issue specific pattern instructions each time; they only need to issue the runway clearance and any necessary spacing or sequencing control instructions.
The phraseology is "Make left/right closed traffic" or "Left/right closed traffic approved."
Military
The military apparently uses two local traffic patterns, a "closed traffic" which is kept close to the field and another one—it might be called the "open" or "outside" traffic pattern—which has much wider crosswind and base legs, so the downwind leg is flown several miles away from the runway.
Therefore in order to achieve the same effect as telling a civilian pilot "left closed traffic approved," I must tell a military pilot "continuous left closed traffic approved" or else they will "request left closed" on every single upwind. If you add that word to your phraseology you might find that they stop bothering you each time.

In your situation, you mention a pilot who said he wanted to "Stay in the pattern." To me this implies a request for closed traffic as the P/CG defines it—he will remain in the closed traffic pattern for multiple landings or low approaches. But if you are confused, you can always ask for clarification!
Other terms you might hear, especially if you are working a radar position, is "option tower" or "option radar." This means the pilot is requesting a clearance for the option and, once they depart, will either remain in the tower pattern or return for radar vectors for another instrument approach.

In the military, the phrase "Closed" simply refers to a 180 degree turn from departure leg to the downwind leg of the traffic pattern.


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What are those polygons on the Garmin avionics navigation display?
I'm not pilot yet, just an enthusiast having some fun in MSFS2020.
What do those colored lines mean in Garmin avionics?

The various lines you see are used to demark certain aspects of the airspace such as controlled airspace (of differing classes) including terminal manouvering areas, restricted areas, military no-fly zones etc.
You get a slightly clearer picture (if you're used to reading sectional aeronautical charts) by looking at the real thing rather than a display on a simulated GPS.

The blue area to the north-west  appears to be SBR-301 which is a restricted area
The magenta area extending mostly North and North-East is the various areas of controlled airspace protecting traffic arriving and departing the various airfields shown to the south
The orange line I'm not too sure about.

Related: What do these polygons mean on VFR charts?


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How does the F-16 engine startup work?
So, the simplest way to start up an F-16s engine is to flip the power switch to "main power" and then set the "jet fuel" switch to "Start 1" or "Start 2".
I have a very simple understanding of the F-16s systems but from what I remember, there is some kind of pressurized gas-bottle, which cranks one of the engine-shafts and gets it to pull fuel from the lines so the engine can be started up.
Is that right and where can I find a detailed set of instructions on how to start up an F-16 (maybe startup and pre-flight checklists) and resources that show how the startup works internally, from the tech side of things.
And if someone here has the knowledge and time, it would be super awesome, if they could also explain what happens, when you go to "main power" (the one before is Batt. and the next also engages the generators i think?!) and then select one of the JFS modes 1 or 2.
This question is asked by a pilot who flies gliders and piston-powered aircraft ;)

Googling "f-16 startup procedure" returns many detailed links. Like this one at f-16.net  https://www.f-16.net/forum/viewtopic.php?t=283

@WPNSGuy's link seems to be useful. Also, you could try the General Dynamics F-16 Fighting Falcon Manual. As of the time of writing, it is sold out on Amazon but there is at least one copy available on eBay.

The START switch routes pressurized hydraulic fluid inside two canisters to the HSM (hydraulic start motor). This motor begins to spin up the JFS (Jet Fuel Starter, a small turboshaft engine) through a geartrain in the airframe-mounted ADG (Accessory Drive Gearbox). Once the JFS is lit and running, it provides torque through the ADG to the main engine through the PTO (Power Take Off) shaft. There are two canisters so that you should ideally get two chances of starting the JFS/engine by discharging one of them each time (START 1), but in certain environmental conditions and fuel types you need to use both cans to get the JFS to start (START 2). Once the JFS is started, it spins the engine up to ~20-25% RPM, and it can keep it up for quite some time. Depending on environmental conditions, the JFS is left to crank the engine for up to 2 minutes.
By lifting the throttle from the cutoff detent to idle, the pilot consents to engage the igniters and introduces fuel to the engine. The JFS continues aiding in spinning the engine until ~50% RPM, then cuts out (and the Start switch springs back to neutral). The engine stabilizes at ~65% RPM idle.
Coming to the MAIN POWER switch, it is used for before start checks to force the plane to use battery power instead of the engine-driven generators (which are not turning anyway) and ground power. The pilot checks that the battery can power the flight control system (FLCS) by pushing the FLCS TEST momentary switch with the MAIN PWR switch on BATT.
The engine may be started on BATT but nothing will be powered, if MAIN power is flipped from BATT to MAIN PWR after engine start the ELEC SYS warning lamp will light up in the annunciator panel. This may be cleared by the ELEC FAULT RESET button.

If this is the explanation, why are there no instruments in the cockpit to monitor the operation of the JFS? When starting, you monitor the RPM of the engine and its FITT. You don't monitor anything on the JFS.

There's not much to monitor about the JFS. It's not operated in flight, and it isn't throttled (you can't select the JFS's speed), so all you need is to make sure it does not overspeed and does not overheat. JFS has monitoring (either mechanical or electronic) to make sure these don't happen. And, remember, an INOP JFS is completely safe, you just have no way of starting the engine. Therefore it is not worth the extra complexity of having gauges etc. to have the pilot monitor the JFS and intervene if necessary, also considering how cramped the F-16 cockpit already is.


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What is the takeoff thrust of a CFM56 engine?
So, to be more clear I currently have an assignment about the Boeing 737-800.
I have to find out the total takeoff distance of the aircraft. I'm using Anderson's book " Aircraft Performance and Design" and I'm quoting that a turbofan engine is affected from the velocity of the aircraft.
Anderson uses this equation: T = k1 - k2*V + k3*(V^2) where k1,2,3 are constants from engine to engine. At his example he uses a Gulfstream IV aircraft and takes the constants as below (chapter 6, example 6.6):
The constants are selected for the takeoff phase. I guess that these values come from the manufacturer but I cant find this type of info anywhere. Not even a number about the takeoff thrust. The only thing that I can find is the maximum takeoff thrust which is the max thrust available from the engines.

Please look into Type Certificate DataSheet of variants you interested.

Given a set of environment conditions: get Vr and Takeoff distance (at TOGA) for three different GW from B737 manuals; then solve a system of linear equations. Those 3 constants are not published and probably Safran's engine model is more complex anyway...

Developing 21,600 to 33,000 pounds of takeoff thrust, the CFM56-5B is the only engine that can power every model in the Airbus A320ceo family.

Safran Aircraft Engines


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Typical burner/combustor dimensions of a jet engine
I know that sounds very generic but lets say for a common engine of a passenger airplane. What could be the typical dimensions for the burner part. I can't find anything online.
Thanks.

Go checkout your local aviation museum?

What if there isnt a local aviation museum?

30-40% the diameter of the first compressor stage is a good estimation for a normal combustor.


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How to calculate CL with the use of MTOW?
I have a problem that it gives us the MTOW of a UAV (200 kg), the speed and the reference area.
So its probably easy to find the CL knowing that it flights at steady level flight (L = W). I'm confused about the use of MTOW. Should we multiply it by the g? (gravity acceleration)
I've done some exercises in the past using lbs as the unit of MTOW and we didnt multiply it with the g. (John Anderson. Aicraft performance and design)
Is it different when using lbs and kgs? I'm confused with the different metric/imperial systems.

I feel you are confused about basic physics (difference between mass and force) rather than SI vs. Imperial units. If your question asks for the CL while the craft flies at that MTOW (a simple approximation), and you can assume some standard air density, then this is an elementary algebra question where you only need to solve the lift equation to obtain the CL. Or it may be a poorly written question that needs you to make some extra assumptions to solve it.

I do understand what you are saying. But I'm a little confused about the use of MTOW. I've seen Anderson uses the equation CL = (2W) / rhoS*V^2 and the W is at lbs. In my case I've got a MTOW of 200kg. Can I use it as 200kg to calculate the CL?

For every equation the left and right side should have the the same units.
For example:
$$ Speed  = \frac{distance \:[m]}{time \: [s]}$$
Or in units:
$$[\frac{m}{s}] = \frac{[m]}{[s]} $$
The same so with the lift equation:
$$L = C_L \cdot \frac{1}{2} \rho V^2 S$$
With units:
$$L [N] = C_L [-] \cdot \frac{1}{2} \: \rho \: \left[ \frac{kg}{m^3} \right] V\left[\frac{m}{s} \right]^2 S [m²]$$
Units only:
$$\require{cancel} [N] = [-] \cdot \left[ \frac{kg}{m^3} \right] \: \left[\frac{m^2}{s^2} \right][ {m^2}] $$
Simplifying:
$$\require{cancel} [N] =  \left[ \frac{kg}{{\cancel{m^3}}} \right] \: \left[\frac{m^\cancel{2}}{s^2} \right][\cancel{ {m^2}}] = \frac{[kg][m]}{[s^2]}$$
Which is correct, link to Wikipedia.
So if you want to use the equation:
$$ L = W $$
Both have to be in $[N]$. You have two options, either have it given to you in Newton, or convert a weight (in $[kg]$) to $[N]$ by using the gravitational acceleration g (in unit $[\frac{m}{s^2}]$ )
I think that the confusion stems from the fact that the unit pound is used in two ways.

for weight called pound (mass)
$$1 [lb] = 0.45359237 [kg]$$
for force called pound (force)
$$1 [\mathbf{lbf}] = 1 [lb] \cdot g
   = 4.44 [N] $$

So if somebody is unspecific and asks what the lift is needed to carry 400 pounds, we don't know if it's way 1. or 2.

For any kind of applied math that you do, the units have to be self-consistent.

For example, we know that gravitational force is:
$$W=mg$$
If you want $W$ in lb [force], and provided that $g$ is given in 32.2 ft/s2, then $m$ has to be provided in slug. If you use kg, then you have to first convert it to slug.

Units can also cancel. Units cancel out when the unit is divided by the same unit.

For example, $\frac{1ft}{1ft}=1$; but if I have in on the denominator, then $\frac{1ft}{1in}=12$, because there are 12 inches in 1 ft.

Back to the lift coefficient, which is unitless. Assuming lift is equal to weight, then
$$C_L=\frac{2W}{\rho V S^2}$$
If $W$ is in lb, then a self consistent set of units would be: $[\rho]=slug/ft^3$, $[V]=ft/s$, $[S]=ft^2$, noting that the definition of $lb=slug*ft/s^2$.
If you have a mass in kg, then an obvious derivation of weight would be to Newton, which is kg*m/s2. So you may have: $[W]=kg*m/s^2$, $[V]=m/s$, $[\rho]=kg/m^3$, $[S]=m^2$.